1. Technical Fields
This invention relates to methods of controlling energization of an electro-magnetically driven valve such as an intake valve and an exhaust valve in an internal combustion engine.
2. Prior Art
With the recent development of computer control technologies, in the field of internal combustion engines, especially for a vehicle, an electro-magnetic actuator has been employed for opening and closing an intake valve and/or an exhaust valve, instead of a conventional cam on a cam shaft driven synchronously with a crank shaft, and, based upon the increase of the degree of freedom of the timing of the opening and closing operations of the valves through use of the electromagnetic actuator, there have been proposed various manners of controlling the operation of an internal combustion engine. Examples of such operation controls are described in Japanese Patent Laid-Open publications Nos. 11-210916, 2000-73800, 2000-234534, 2000-337177, 2001-182570, 2001-193504, 2002-81329, 2002-81569.
FIG. 1 in the accompanied drawings shows a general and schematic sectional view of an electro-magnetically driven intake valve, which is similarly shown in FIG. 2 of the Japanese Publication No. 2001-193504 based upon an application filed by the same applicant as the present application. In this drawing, an opening end of an inlet port 26 is fringed with a valve seat(s) 200 and opened and closed by a valve body 28a. The valve body 28a is carried by a valve shaft 28b, and in this figure, a valve guide 201 guides the valve shaft 28b so that the valve shaft can move up and down, and thereby, the valve body 28a is moved between opened and closed positions by electromagnetic driving apparatus generally denoted by 30.
The electromagnetic driving apparatus 30 has a housing 300, within which incorporated are a valve-closing electromagnetic apparatus consisting of valve-closing cores 301 and valve-closing coils 303; a valve-opening electromagnetic apparatus consisting of valve-opening cores 302 and valve-opening coils 304; an armature 305 carried on the valve shaft 28b and movable between the valve-closing and valve-opening electromagnetic apparatuses; and compression coil springs 306 and 307. As shown in the drawing, the compression coil springs 306 and 307 bring the armature 305 to an intermediate position between the two electromagnetic apparatuses when neither of coils 303, 304 is energized.
In the example as shown here, an intake valve lift sensor 40 is mounted directly on the electromagnetic driving apparatus 30. This lift sensor has a housing 400, mounted on the housing 300 of the electromagnetic driving apparatus 30; a disk-like target 401, mounted on the upper end of the valve shaft 28b within the housing 400; and a gap sensor 402 attached on the housing 400, while facing on the target 401, and detecting the displacement of the target.
Further, although not shown in the drawing, in such an electro-magnetically driven valve used as intake and/or exhaust valves, in general, a slip joint is incorporated near the lower end of the valve shaft 28b, namely the coupling portion with the valve body 28a, which slip joint enables the distance between the valve body and armature to expand and contract very slightly. This slip joint is provided for avoiding a condition that, if the armature is fixedly connected to the valve body, the support of the armature flush against the valve-closing cores 301 and coils 303 would prevent the tight sealing of the valve body to the valve seat, when the valve body is forced on the valve seat by the pressure within a cylinder during compression and explosion strokes.
The control of operation of opening and closing this type of electro-magnetically driven valves is done by controlling energization of valve-opening and/or valve-closing coils. In this case, generally, the operational states of an electro-magnetically driven valve, used for either of an intake valve or an exhaust valve, are either of an open state or a close state, and any states in between are transient unless any special control of opening and closing a valve is done. Thus, usually, an electro-magnetically driven valve, when operated, is held in either of a full opened position, in which an armature is adhered to an valve-opening electromagnet consisting of valve-opening coils and cores, or a full closed position, in which the armature is adhered to an valve-closing electromagnet consisting of valve-closing coils and cores, by feeding a weak holding current to the valve-opening or valve-closing coils except during opening or dosing the valve. When the valve body is moved from the full dosed position to the full opened position, the holding current for the valve-dosing coils is turned off first (usually, a reverse current is subsequently fed to the valve-dosing coils), and then, under the action of springs, the valve body and armature start moving to the valve-opening side in unison. Thereafter, when the armature reaches to a position near an intermediate point between the valve-opening and valve-dosing electromagnets and the distance between the armature and valve-opening electromagnet is shorten enough for the valve-opening electromagnet to function effectively through energization of the valve-opening coils, the energization of the valve-opening coil is started. Similarly, the valve is moved from the full opened position to the full closed position.
In general, when a valve body is started to move from a full closed position to a full opened position or from the full opened position to the full closed position, its moving speed increases gradually together with its displacement (Usually, as an armature moves closer to an electromagnet, its electromagnetic force attracting the armature increases.). Preferably, however, the moving speeds of the valve body and armature is to be reduced to almost zero by the end of the opening or closing operation of the valve, for avoiding violent collision of the armature against the coils and cores of the valve-opening and/or dosing electromagnets at the end of the opening or closing operation of the valve body; and violent collision of the valve body against a valve seat in dosing the valve. On the other hand, in order to complete the opening and closing operation of the valve quickly, preferably, the moving speeds of the valve body and armature are to be increased in the intermediate portion of the opening and closing movement of the valve.
From the above, it is generally recognized that the moving speed of a valve body or an armature is preferably to be varied with the displacement of the valve body or armature as shown in FIG. 2. In FIG. 2, an example of speed change in opening a valve is shown, wherein the abscissa is the displacement of a valve body or armature, namely Lift (the distance between the valve body and valve seat) and the ordinate is an opening speed, namely, the moving speed of the armature or valve body during opening. For varying the moving speed with lift as shown in FIG. 2, exciting current to be fed to coils (valve-opening coils in this case) is made varied with the position of the valve body or armature along a profile as shown in FIG. 3.
In this connection, mathematically speaking, the concepts defined as “distance”, “movement” and “speed” each have positive and negative values, and in matters of the opening and closing of a valve as in the present application, the distance, movement and speed are regarded as positive or negative, depending upon the direction of the movement of a valve body; but, since the present objects are to consider how opening and/or closing operations of a valve body are made quick and how the movement of the valve is terminated at the end of the operation without impact, the displacement of the valve body or armature, represented with lift as shown above, and the moving speed of the valve body or armature in the direction of increasing the displacement are defined as positive.
Furthermore, in order to obtain the relation between the displacement and moving speed of a valve body or an armature as shown in FIG. 2, exciting current fed to coils is controlled in connection with the displacement through combination of a feedforward(FF) control and a feedback (FB) control. In this case, first, the exciting current is controlled with the FF control for setting an actual moving speed for a target moving speed as shown in FIG. 2 (the profile in FIG. 3). A deviation of an actual moving speed from the target, when generated, is (expectedly) cancelled by correcting the exciting current through the FB control based upon the value of the deviation. Usually, based upon a deviation of an actual moving speed V from a target moving speed Vt, ΔV (=V−Vt), an amount of FB control for exciting current is given by −Gb·ΔV, where Gb is a positive FB control gain. Thus, when ΔV is positive, namely, when the actual moving speed exceeds the target moving speed, the control of the exciting current is done by subtracting Gb·ΔV from the corresponding FF control amount. In one case, an FB control gain Gb is constant, and in other cases as described in the above JP No. 2000-23454, an FB control gain is increased as the distance of spacing between an armature and an electromagnet attracting the armature (spacing distance) increases. In JP No. 2002-81329, it is proposed to define fields in accordance with the ranges of deviation ΔV and spacing distance and to execute a feedback control using a different FB control gain for each of the fields.
By the way, since an FB control amount is given by −Gb·ΔV as described above, it can be understood that, the larger the FB control gain is, the higher responsibility or sensitivity of the control, namely, the higher control speed is obtained, thereby increasing the effect of the FB control. The increase of the control speed, however, often causes an excessive control inducing hunting in the control. On the other hand, if an FB control gain is excessively small, the longer time would be required for making an actual moving speed in conformity with a target moving speed, or the moving speed at the end of the movement would not reach to the target moving speed that would be an appropriate value.
Further, in the speed control of the opening and closing operation of an electro-magnetically driven valve: the controlled object of the present invention, the importance and/or necessity of FB control varies, dependent upon the relation between actual and target moving speeds, such as the direction and magnitude of the deviation between the actual and target moving speeds. As already described, in order to prevent violent collision between a valve seat or an electromagnet and a valve body or an armature resting thereon (at the end of an opening or closing operation), a target moving speed is so set that the speed at the resting becomes substantially zero. For example, however, in a case that an actual moving speed exceeds its target value, it is enough that the speed at the resting is within a certain satisfactory range and there is little need to urgently correct the actual moving speed through FB control (it is possible that the reduction in the time for opening and closing a valve is preferable.). On the other hand, when an actual moving speed is lower than its target one, it is possible that the moving speed has become zero before an armature reaches to electromagnets. In this case, the armature will be pulled back by springs, and thereby, the armature and a valve body are floating around the intermediate position between opened and dosed positions, inducing a very serious problem of stepping-out of operation of an intake valve or an exhaust valve. In order to avoid such a stepping-out condition, it is required that an actual moving speed can be corrected quickly through FB control without inducing the control hunting.
Accordingly, in the control of opening and closing speed of an electro-magnetically driven valve, an FB control gain should be set taking into account the necessity of FB control based upon the relation between actual and target moving speeds so as to avoid the control hunting and stepping-out condition.
Further, it is possible that a target moving speed or an FF control amount (current fed to electromagnets If given in accordance with the profile in FIG. 3) does not match characteristics of an actual electro-magnetically driven valve due to aging variation of the valve or an individual difference of products, and thereby, the magnitude (absolute value) of an FB control amount would be enlarged. In other words, while a target moving speed and/or an FF control amount is predetermined values based upon the characteristics of an electro-magnetically driven valve, it is possible that the predetermined target moving speed would turn incompatible with the characteristics of an actual valve because the actual valve has a plurality of frictional sliding portions, electromagnets, springs, etc., the conditions and characteristics of which elements can vary from those at the manufacturing thereof. Also, in actual products, some differences of performances among the products are inevitable so that a target moving speed predetermined based upon designed characteristics can be incompatible with actual characteristics of a valve. Then, it would be difficult to make an actual moving speed in conformity with its target moving speed, resulting in the increase of the deviation ΔV and consequently, the increase of an FB control amount. This, in turn, would increase the fear of occurrence of the control hunting as described above. Accordingly, in order to reduce the fear of the hunting due to FB control and to make an actual moving speed in conformity with its target value quickly, it is preferable that a target moving speed and/or an FF control amount can be corrected, compensating for aging variation of an electro-magnetically driven valve and the other conditions thereof.
Further, while a function determining (calculating) an FB control gain Gb is set out upon manufacturing or designing an electro-magnetically driven valve, it is possible that an FB control amount is insufficient to make an actual moving speed in conformity with its target moving speed because of aging variation and/or individual differences among products, as described above. Thus, it is preferable that a function and/or means for determining FB control gain Gb can be corrected appropriately after starting of use of an electro-magnetically driven valve.
Moreover, during use of an internal combustion engine, intake/exhaust valves are directly exposed to pressure variation of operational fluid in cylinders, and thus, the movements of valve bodies are subject to acceleration and deceleration forces from the operational fluid. Acceleration and deceleration forces are advanced by first order from a moving speed to be controlled, and accordingly, are not directly reflected in −Gb·ΔV. Thus, more appropriate speed control will be achieved if effect of pressure of operational fluid is taken into account in control of an FB control gain.
Furthermore, as already noted, in the energization control for electro-magnetically driven valves described in some of the above-listed patent publications, it has been proposed to selectively and appropriately employ different FB control gains depending upon the distance between an armature and (energized) electromagnets or deviation (ΔV) between an actual moving speed and a target moving speed, rather than an always constant FB control gain. In order to avoid the control hunting and/or stepping-out of control, however, it is desirable that deviation ΔV or else is corrected quickly and gently without abrupt change of an FB control gain.